This invention was made with government support under Cooperative Agreement: NCC2-9016 for the Variable Geometry Advanced Rotor Technology program awarded by NASA. The government therefore has certain rights in this invention.
The present invention relates to an elastomeric coupler assembly, and more particularly to a reversible elastomeric coupler assembly, which converts an axial displacement input into a rotary output.
Multi-element airfoils are in common use on fixed wing aircraft. Such applications, however, are either in a fixed configuration or activate at relatively slow rates. In conventional applications the aerodynamic flow environment is steady or quasi-steady.
Actuators for multi-element airfoils, such as aircraft leading edge slats, are relatively well known. Such actuators commonly employ a mechanical linkage or track, which provides for translation and pitching of the slat relative to the wing. Aircraft slats are deployed from a leading edge of a wing and may be powered between an extended and a retracted position. As the wing is fixed and maintains a fixed relationship with the aerodynamic flow environment, actuation of the slat is relatively straightforward. Moreover, the speed of slat actuation is of little concern, as the slats are commonly employed for distinct flight conditions such as landing and takeoff.
Multi-element airfoil application to rotary-wing aircraft has concentrated upon the development of fixed elements, as actuation of an active element upon a rotor blade provides multiple complications. Such complications include withstanding the high forces upon the mechanical connection between the fixed element and the movable element, and the requirement for high bandwith and high load actuation for slat deployment and retraction. It is further desirable that the coupler be of light weight, while providing the capacity to actuate the movable member multiple times within a single rotor revolution without concern for rotor blade azimuth position. Such requirements are without correlation in a conventional fixed wing multi-element airfoil.
Accordingly, it is desirable to provide for the actuation of a movable element that overcomes the many complications inherently associated with a rotary-wing application.
The elastomeric coupler assembly, according to the present invention, movably supports an active slat relative to a main element. An inner elastomeric coupler assembly and an outer elastomeric coupler assembly support the slat therebetween. An actuator rod extends within the main element, from the blade root portion to the inner elastomeric coupler assembly, to actuate the slat. Centrifugal force operates to drive the slat to a first position and the actuator rod operates in tension to pull upon the inner elastomeric coupler assembly to drive the slat in opposition to the centrifugal force to a second position.
Each elastomeric coupler assembly includes a grounding member and an active member. The grounding member is fixed to the main element. The active member supports the slat. The active member is movably mounted to the grounding member through a helical elastomeric bearing, and a first and second elastomeric support bearing.
The elastomeric bearings include a plurality of shear deformable elastomeric layers attached between high stiffness shims, which act as geometric constraint layers. The elastomeric bearings support rotation of the slat about a virtual hinge axis. The slat rotates and translates relative the main element. One elastomeric support bearing operates to carry the nominal upward lift upon the slat, while the second elastomeric support bearing operates to support the slat in the event that there is a download on the slat. Download may occur when the outboard portion of the main element operates at a negative angle of attack, i.e., when the outboard portion of the blade xe2x80x9cdigs-inxe2x80x9d.
The helical elastomeric bearing is layered such that it defines a section of a circular helix, which encircles the virtual hinge axis. The helical bearing acts as a two degree of freedom coupler, which in the present embodiment converts a linear input parallel to the virtual hinge axis into a rotary output about that axis. A force applied to the active member results in additive incremental shear deformation of the elastomeric layers. The shear deformation is constrained by the high stiffness helical shims and consequently the active member is guided along a translation and rotation trajectory defined by the helical structure of the layered bearing. The helical bearing is a reversible coupler, in that a torque applied to the active member, forcing rotation of said member, will result in a coupled translation of the active element, as defined by the helical geometry. Virtually any coupling between linear or rotary degrees of freedom will benefit from the present invention.
In operation, centrifugal force operates to slide the slat outboard toward the blade tip. The elastomeric support bearings of the elastomeric coupler assemblies provide minimal shear resistance to this sliding movement. That is, the support bearings provide independent degrees of freedom in slat rotation and translation. In the helical elastomeric bearings, the rotation and translation degrees of freedom are not independent, because the high stiffness shim layers are helical and thereby constrain the elastomeric deformation of the elastomeric shear deformable layers to a predetermined coupled rotation about the virtual axis and spanwise translation. The active member of the helical bearing moves relative to the grounding member by virtue of successive shear of the elastomeric layers along a helical path between a support ramp and a mating ramp.
Outboard sliding of the slat is accommodated by the active member and the attached slat moving elastomerically along the helical arc of the helical elastomeric bearing, such that the slat rotates nose down. This arrangement negates the need for a safety interlock as in the event of a hardware/software failure, an actuator need only be vented and the slat will achieve its deployed position. Moreover, as centrifugal force operates to drive the slat to a deployed condition the slat requires powered activation for only one direction. Physical xe2x80x9cstopsxe2x80x9d limit the motion envelope of the slat.
To retract the slat, the actuator operates to pull the actuator rod and translate the active member inboard. As the active member is translated inboard, the helical bearing structure forces the slat to rotate nose up. The helical coupling induced rotation of the active member relative to the grounding member retracts the slat into the nose up position. Preferably, the controller controls the actuator to drive the slat to a desired position under prescribed or active control.
The present invention, therefore, provides a coupler, which advantageously accommodates the high centrifugal forces of a rotary-wing application, while providing high power actuation forces with high rates of deployment and retraction. The coupler is light, yet provides the capacity to actuate the movable element multiple times within a single rotor revolution without concern for rotor blade azimuth position. In addition, no sliding or rolling interface between the movable and fixed element is required. Motion is accomplished through deformation of the constrained elastomers. No lubrication or sealing is required which greatly reduces maintenance requirements and increases reliability.